[lanxe]

HI,

I just got an Otari MX5050 MKIII-2 (2 for two track) 1/4" tape machine in the mail. I was told it was in fine working condition....>but of course it is not.

At first i had many problems........but i have fixed most of those. My only problem now is with the play speed (and record speed). the capstan and pinch roller work 100% with the tension arm and safety switch. Fast forward works fine (turns on right take up reel at the right speed). Rewind works fine (turns on left supply reel at the right speed).

but when i push play both the supply reel and the take up reel turn on as if i pushed fastforward and rewind at the same time (both motors spin slightly slower than if i were to push fast forward or rewind, but not much slower). the motors are spinning fast and in the opposite direction (right, takeup reel spins counterclockwise, left supply reel spins clockwise). WHAT THE HELL?

does anybody have a schematic or more info than what is on otari's website?

i assume that the motor speeds are controlled by voltage......so is there an adjustment for this voltage?

the seller is being cool and is going to send a parts machine, so i should have some spare parts but i would like to have a place to start.

i traced the motor wires back to the pcb that is right between them. its a rather simple pcb, looks like its where the motor power is coming from. connections are fine to that board.

thanks guys,
Ryan

[SSLtech]

but when i push play both the supply reel and the take up reel turn on as if i pushed fastforward and rewind at the same time (both motors spin slightly slower than if i were to push fast forward or rewind, but not much slower). the motors are spinning fast and in the opposite direction (right, takeup reel spins counterclockwise, left supply reel spins clockwise). WHAT THE HELL?

Believe it or not, that sounds exactly right, as I read your description.

You need backtension, so the supply reel pulls backwards.

You need takeup, so the takeup reel turns forwards.

unloaded, they will speed up to approaching fast-wind speeds... but it's not the SPEED similarity that matters, it's the TORQUE. Try holding the spool while you hit play, You should find that the FORCE of the motor is vastly less, even though the final -unloaded- speed is similar.

How do you know that the pinch roller is good? -Is it running fast or slow, and is the tape gummy?

Unless you have a mildly catastrophic error, most machines will play on-speed reliably, but an aging pinch roller, or a polished capstan, coupled with friction from old tape, and you've got speed problems.

-Do you even have tape on it, or are you trying to suss it out without tape and are letting yourself make erroneous assumptions perhaps?

Keith

[lanxe]

I guess i should put some tape in it and just go for it!!!! i worry because the machine came to me with lots of problems and it took alot to get it to where it is (and i second guess my own work)

I know i need back tension...........but man, these things are spinning fast! i had the same machine a couple of years ago, and it didnt seem to whip around like this, even without tape.

Thanks for the advice though.........it gives me the courage to throw some tape on there and see if i am just making erroneous assumptions
......i really hope so. :oops:

i guess why i worry about this is because it seems like making the motors over torque may overheat/overwork them or stretch or break tape.  

its probably just my lack of experience.

thanks keith, you have always been more than helpful when i ask dumb questions.

Ryan

[SSLtech]

Just try putting it into play while a single finger tries to keep the reel from starting to turn. If you can hold it with a finger, the tape is safe.

Even light torque will make the reels run fast, it just won't accellerate[/u] them as quickly. There's so little frictional resistance (almost no air friction, and nice bearing races) that the speed limit (where the motor can no longer accellerate due to magnetic considerations, hence the speed that the reel motor finally attains) is about the same at low torque or high torque... but the PULL of the motor is very different.

Basically, if you don't give the motor anything to 'fight', it will get to more or less the same speed. If you make it fight, the speed difference will be considerable... night & day difference!

If you want to measure it, use a spring gauge (a fish-weighing gauge.. whatever they're properly called...) and some string wrapped around the NAB center. Given the radius of the center and reading the "weight" of the force which the motor can exert, you can determine the static tension on the tape. It should be very different from play to fast wind.

Keith

[lanxe]

thanks keith,

i did what you said and the decided on putting some tape on there. it WORKS! thanks! man, i feel like an idiot, but this is really my first experience with tape.  :oops:

one question though, i am hearing a mechanical pulse from the physical tape (not in the monitors, just from the machine). it pulses about every 1/2 to 1 second. it seems like it may be the tension on the tape changing......i will have to dig deeper into it i guess


thanks again,
Ryan

[KingKai]

Ryan,

See if the mechanical noise is in synch with either reel. This sounds like reel to tape scraping to me. It dosen't take much to be annoying. Reel warpage is usually the culprit. This is made worse if the reels are not locked down by either a rubber puck or the nab hubs depending on the reel size in use.

Hope this helps,

Peace - Out, Irv

[lanxe]

yeah, i really like playing around with this machine. i appreciate all of your help getting me up to speed with tape!

i need to learn the calibration/alignment procedure now. it doesnt seem too hard though (but i do need to get some 1/4" cal tape)

thanks,
Ryan

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